1. Field of the Invention
The present invention is directed to an ultrasonic solder bath which has a container to hold molten solder, at least one ultrasonic transducer to create ultrasonic waves, a probe connected to each of the transducers and means for mounting the probe to extend through a wall of the container into the bath which wall is preferably the bottom wall of the container.
2. Prior Art
A soldering device for a flux-free soldering operation by means of ultrasonic waves is explained and described in U.S. Pat. No. 3,385,262. As disclosed, the soldering device of the patent consists of a container which holds a bath of molten solder and a probe or ultrasonic horn, which extends from a source such as an ultrasonic transducer, is brought into the bath through either the bottom wall of the container or, in one embodiment, through a side wall. The ultrasonic waves, which are generated in the ultrasonic transducer, are carried by the probe or horn and adjacent the end surface create an intense activation in the molten solder which causes the improvement of the wettability of the parts to be soldered due to cavitation of the solder. One of the problems discussed in the patent is the problem with the contamination of the bath due to the formation of oxides on the surface of the bath which contamination is the problem with all open solder baths.
One approach for dealing with the contamination such as oxides at the surface of the solder bath is disclosed in FIG. 3 of German Pat. No. 23 52 595. As disclosed in this German patent, the bath of solder is contained in a container, which is closed on all sides with the lid of the container being provided with a chimney or shaft, which extends directly into the bath of molten solder. By means of an application of a pressurized gas such as an inert covering gas, it is possible to elevate or lift the level of the solder in the chimney or shaft in such a fashion that the solder level forms a kind of meniscus at the upper end of the chimney. If the gas pressure acting on the solder is reduced, the solder level will fall back again. The solder zone therefore can be the plane as formed by the upper edge of the chimney. Such a soldering device has shown great merit. If one positions an imersion probe of an ultrasonic transducer in the chimney or shaft in order to improve the wettability of the parts to be soldered to each other, there is however the disadvantage that tin oxide will be deposited on the surface of the probe when the level of solder is reduced. If one positions the end of the imersion probe of the ultrasonic transducer below the lowest level of the solder in the shaft, the activity of the ultrasonic waves is thereby reduced. This has a result that it is no longer possible to freely raise and lower the solder level in the chimney as desired.